A steam generator is a closed, heated vessel or a pressurized pipe system which serves the purpose of generating steam at high pressure and high temperature for heating and operation purposes (e.g. for operating a steam turbine). At especially high steam power and pressure, such as during energy generation in power stations for example, water tube boilers are used in such cases, in which the flow medium—usually water—is located in steam generator tubes. Water tube boilers are also used with solid-fuel combustion, since the combustion chamber in which heat is generated by combustion of the respective raw material can be designed in any given manner by the arrangement of pipe walls.
This type of steam generator constructed as a water tube boiler thus comprises a combustion chamber, the peripheral wall of which is formed at least partly from pipe walls, i.e. gas-proof, welded steam generator pipes. On the flow medium side these steam generator pipes initially form an evaporator, into which the unevaporated medium is introduced and evaporated. The evaporator in such cases is usually arranged in the hottest area of the combustion chamber. Connected downstream from it on the flow medium side might be a device for separation of water and steam and a superheater, in which the steam is heated further beyond its evaporation temperature, in order to obtain a high level of efficiency in a following thermal power machine, such as a steam turbine for example. A preheating device (so-called economizer) can be connected upstream from the evaporator in the upstream generator, which preheats the feed water by utilizing the waste or residual heat and in this way likewise increases the efficiency of the overall system.
Depending on the design and geometry of the steam generator, further steam generator pipes can be arranged within the combustion chamber. These can be combined or welded into an inner wall for example. Depending on the desired arrangement of steam generator pipes or inner walls within the combustion chamber, it can be necessary in such cases to connect inner walls on the flow medium side behind one another and to connect their steam generator pipes via an intermediate collector. In the intermediate collector the medium flow from the upstream inner wall is merged and serves as an inlet collector for the downstream inner wall.
In specific operating states however a steam content greater than zero can be produced in the intermediate collector. With such a steam content an even distribution of the medium to the downstream inner wall is not possible with a simple collector, so that water-steam mixture separation can occur. Individual pipes of the downstream inner wall can thus already have such a high steam contents or enthalpies at their inlet that an overheating of these types becomes very probable. Such an overheating can lead in operation over the longer term to pipe damage.